Transparentized paper and method of making



United States Patent TRANSPARENTIZED PAPER AND METHOD OF Benjamin F. Aycock, Elkins Park, and Louis E. Kelley, Wyncote, Pa., assignors to Rohm & Haas Company, Philadelphia, Pa., a corporation of Delaware No Drawing. Application March 26, 1954, Serial No. 419,116

15 Claims. (Cl. 117-155) This application relates to the treatment of fibrous materials, and especially paper, and methods for transparentizing them.

Various compositions have been used heretofore for the transparentizing of papers, such as oils. While the oils do transparentize the paper sheets, they are generally accompanied with the production of an oily surface feel and on ageing, they lose transparency and frequently become embrittled, yellowed and strcaky or blotchy;

When vegetable oils are used, rancidity is encountered. When such papers are heavily oiled as is required for certain purposes, they are not receptive to writing either with ink or pencil and generally some of its oily content is transferred to other materials that come into contact with the transparentized sheet. When such papers are used as tracing papers, they generally yellow on ageing and, therefore, absorb ultraviolet light which causes them to give poor prints. Various resins have been used to transparentize papers but many of them sufier from various disadvantages or difiiculties including poor penetration and the tendency to deposit a heavy surface coating.

The papers thus transparentized are frequently reducedin flexibility unless plasticizers are employed, but the use of plasticizers is subject to the disadvantage of embrittlement on ageing as a result of the loss of the plasticizer.

Resin-treated papers frequently are'subject to the development of stars, streaks or blotches of opacity on ageing;

they sometimes fracture when a pencil of 4H to 6H hardness is used to write on them, and erasures made on tracing papers of this type often cause the development oflines or ghosts on blueprints.

It is an object of the present invention to provide an improved composition and treatment for transparentizing fibrous products and particularly paper, which is capable of imparting a high degree of transparency to the paper or the like and which is permanent and does not detract from the flexibility and foldibility of the paper. A further object is to produce transparent papers which have improved receptivity to ink and pencil and can be erased without damaging the paper or its reproduction qualities. Other objects and advantages of the invention will be apparent from the description thereof hereinafter.

; The term transparency herein used is meant to include not only a substantially clear sheet which transmits light with little or no diifusion thereof, but also sheets which are translucent and serve to diffuse the light transmitted to a certain extent. In the broad sense used herein, the term transparency refers to a loss of opacity of such character as to enable the easy reading of typewritten, printed, or handwritten matter on a base upon which the transparentized sheet is directly superimposed. In some situations, it is desirable that this transparency be accompanied with a diffuse transmission and reflection of light, such as in lampshades and in tracing papers. In other uses, such as in window envelopes, a more completely transparent condition, in which little or no diffusion of transmitted and reflected light occurs, may be preferable.

According to the present invention, the fibrous sheet material that is to be transparentized is treated with a composition that comprises a predominant proportion of 2,765,243 Patented Oct. 2,1956

a monohydric or dihydric alcohol having a large hydrophobic group of from 8 to 24 carbon atoms. The composition also contains a highly reactive methylolated urea which has been alkylated by means of methyl, ethyl or isopropyl alcohol to a sufiicient extent to render the methylolated urea compatible with the high molecular Weight alcohol. After application to the fibrous sheet, the alcohol and urea derivative are caused to react in the presence of heat and/ or acid catalyst so as to set or fix the alcohol in situ in the fibrous sheet. In this manner,

. the transparentizing action of the high molecular weight alcohol is rendered permanent since the reaction with the urea derivative increases its molecular weight to such an extent as to prevent subsequent migration of the alcohol out of the fibers. The resin imparts hardness to the paper and enables it to receive ink and pencil and to be erased without fracturing and without showing ghost images in photographic reproductions at the points of erasure. The alcohol acts as an internal plasticizer for the resin.

, The high molecular weight alcohol comprises a hydrophobic group of 8 to 24 carbon atoms which renders the alcohol highly penetrative of the fibers. The hydroxyl groups in the alcohol serve to provide a functional group capable of reacting with the urea derivative to set or fix the alcohol permanently in the fibers as a high molecular weight compound permanently bound up in the fibers. Since the urea derivative lacks the large hydrophobic groups required to facilitate penetration of the fibers, the high molecular weight alcohol serves as a carrier for the urea derivative. The low vapor pressures of the high molecular Weight alcohols have the additional advantage of minimizing loss of the alcohol by evaporation during the reaction of the high molecular weight alcohol with the urea derivative which is generally effected by heat. The preferred monohydric alcohols are those which contain a hydrophobic group having 8 to 12 carbon atoms and the preferred dihydric alcohols contain a hydrophobic group containing 12 to 24 carbon atoms. Examples of the alcohols that may be used either individually or as a mixture of two or more thereof include n-octanol, 2-ethylhexyl alcohol, lauryl alcohol, myristyl alcohol, hexadecyl alcohols, stearyl alcohol, oleyl alcohol, phenylethyl alcohol, naphthenic alcohols, such as tetrahydro-a-naphthol, decahydro-fi-naphthol, fatty acid monoglycerides, e. g., glycerol monostearate, glycerol oleate, glycerol palmitate, and the monoglyceride of the The alkylated methylol urea may be obtained by condensing a mixture containing 1.5 to 3 moles of formaldehyde per mole of urea and then alkylating the resulting methylolated urea sufiiciently to make it compatible with the high molecular weight alcohol. On the average, a minimum of at least one half mole of the methanol, ethanol or isopropanol should be combined per mole of urea. In the case of methanol and ethanol, all of the hydroxyl groups of the methylolated urea may be etherified with the alcohol. However, with isopropanol, it is'preferred to leave some of the hydroxyl groups unetherified. It is essential that the methylolated urea be at least partially etherified to render it compatible with thehighmolecular Weight penetrative alcohol, and it is important that the ethen'fication be efiected with low molecular weight alcohols to avoid the production of large molecules which are not readily carried into the fibers by the penetrating action of the high molecular Weight alcohol. In addition, and for the same reason, the alkylated methylolated urea should not be appreciably polymerized. In any event, it should not be carried beyond an average molecular weight of 500. These factors are important also to avoid the production of excessive amounts of resins on the surfaces of the fibers.

The treating composition may comprise from 55 %70% by weight of high molecular weight alcohol and from 30%45% by weight of the alkylated methylolated urea. Preferably, the composition comprises 58-63 parts by weightof the high molecular weight alcohol combined with 42 to 37 parts by weight respectively of the alkylated methylol urea. Such compositions are liquid and many of them are of adequately low viscosity to penetrate rapidly fibrous sheets, such as paper. If desired, however, a solvent for the alkylated urea and alcohol may be added to dilute the composition to a concentration of from 40%90% by weight of non-volatiles. Even a small amount of dilution generally improves the penetration markedly, especially when the undiluted compositions are viscous. Suitable solvents include methanol, ethanol, isopropanol, butanol, the diethyl ether of diethylene glycol, Z-ethoxyethanol, the butyl ether of 2-ethoxyethanol, the acetate of Z-methoxyethanol, and mixtures thereof with other solvents, such as aromatic hydrocarbons. For example, a mixture of isopropanol with water or with toluene or with benzene, in 1:1 proportions in each case, may be employed. Generally, however, better results are obtained with substantially anhydrous solvents.

The composition should contain a catalyst of acid character to accelerate the reaction of the high molecular weight alcohol with the alkylated methylol urea. This catalyst may be a residual catalyst left in the urea derivative after alkylation, or it may be added or substituted for each catalyst. The preferred catalysts are Strong mineral or organic acids, such as hydrochloric acid, sulfuric acid, phosphoric acid, p-toluene-sulfonic acid, ethanesulfom'c acid or the like. From 0.2 to 2% of acid catalyst may be used based on the combined weight of high molecular weight alcohol and urea derivative. Preferably about 0.5% to 1% is employed and it is preferable to incorporate the catalyst into the composition shortly before use so as to avoid increase in viscosity and corresponding reduction in penetratability of the composition.

The composition may be applied to many types of fibrous materials such as sized or unsized paper, whether made from rag base stocks, sulfite stocks, kraft stocks or mixtures. The weight of the paper may vary widely depending upon the end use. For example, a thin 8 to 12 pound stock may be used for making the transparent windows of window envelopes. Somewhat heavier stocks such as l2-pound to l8-pound papers'may be used for making tracing papers and even heavier stock may be used for making lampshades. For the latter purpose, the paper sheet may be a parchment sheet or even Woven or non-woven cloths. Instead of a single thickness, such heavier sheets may comprise'a laminar structure.

The amount of the transparentizing composition that is applied to the paper may vary from %30% or more based on the initial weight of the paper. The amount required depends upon the degree of transparency required as well as upon the thickness of the paper. For making tracing papers, it is preferred to apply from l0%-30% by weight of the transparentizedcomposition to obtain the desired translucency.

The composition may be applied to the fibrous sheetin any manner desired. Conventional impregnating equipment may be employed such as those which pass the sheet over an immersion roll which transfers the composition'from -a bath thereof to one. side of the .sheet.

The sheet may be passed through the bath so as to pick 4 up the composition on both surfaces, or it may be applied to one or both surfaces by rolls, brushes, sprays or any other system. After application to the sheet, the impregnated sheet may be passed between scrapers and/or squeeze rolls to enhance penetration and to get rid of excess coating materials. Doctor knives or rods may be used for the same purpose. Smoothing devices may also be employed Whether of rotary or stationary type,

such as a smoothing roll or rod.

After impregnation of the sheet, it is necessary to effect reaction between the high molecular weight alcohol and the alkylated methylol urea either immediately or preferably after standing or ageing, for example in the form of a wound roll or a stacked pile of sheets, for several hours to several days, for example overnight. Such ageing tends to equalize the distribution of the transparentizing composition through the paper. The reaction is usually performed by heating to a temperature of 120 -300 F. for periods which vary from 10 minutes to 10 seconds respectively. If the composition is applied with the aid of a solvent, additional time may be needed to eifect removal of the solvent before the reaction or curing. The drying and curing may, of course,

be performed simultaneously by passing the treated sheet over heated rolls at the appropriate temperature, or through a drying oven containing heated air at the appropriate temperature. Generally, the time required for curing varies inversely with the temperature. However, for a given temperature, the time may be shortened by increasing the proportion of catalyst and vice versa. For example, a curing period of 10 to 30 seconds may be employed for curing a l2-pound tracing paper treated with about 20% of the composition, 10 seconds being adequate when 2% catalyst is used, but 30 seconds being required when only 0.5% catalyst is used. The curing is necessary to prevent loss in transparency and embrittlement on ageing, and it also insures water resistance of permanent character. Not only does the curing improved drawing surface impart permanency to the transparency and resistance to water, but it is essential to impart flexibility,.high folding endurance, ink and pencil receptivity and erasibility. When properly cured, tracing papers in effect have an since the cured reaction product permeates every fiber of the sheet. Pencils of standard hardness can be used without excessive pressure or wear. Erasures do not destroy the drawing surface, and

ink lines drawn over erasures do not feather or blot.

The following examples illustrate the invention. The parts given therein are parts by weight except where otherwise noted, and the transparency was determined by a system in which a sample of the paper to be tested is placed successively in contact with a white background in the form of a MgCOs plate and then a black .background. Light from a standard light source of a test unit (containing a blue filter) is directed through the paper to the background and then back to a photometric detector system. The scale of the latter system is set to 100 for the standard plate of magnesium-carbonate when no paper intervenes. with the white background but as the paper is transpar entized the light is absorbed by the black background and thereby gives a measure of transparency. The system is based on the following principles:

Reflectance with black background 1 0: t Reflectance with white background X 0 opam y l00-percent opacity=percent transparency Example 1 This test measures the reflectance pH of the mixture is readusted, and the mixture is then heated at 70-75 C. for 20 minutes. The mixture is treated with a solution of phosphoric acid in methanol to a pH of about 3.5 and heated under reflux for 15 minutes. The mixture is cooled to 55 C. Alkali solution is added to bring the pH to 7.2 and the mixture heated under reduced pressure to remove the bulk of volatile materials. The product is a clear, practically colorless syrup having a viscosity of G on the Gardner-Holdt scale at 70% solids.

The methylated methylol urea syrup (50 parts) is mixed with 50 parts of dicyclopentenyl alcohol and one part of p-toluene sulfonic acid is added to themixture. A 12-pound 100% rag tracing paper base is passed through a roll coating machine over a coating roll running partially immersed in a trough containing the above mentioned mixture, then over scraper bars or through squeeze rolls, and over a smoothing roll. The impregnated paper which contained about 25% of non-volatiles was aged overnight and then cured at 250 F. for 20 seconds. The resulting paper had a tack-free surface and its transparency was 65%. Its foldability was greater than the untreated paper and increased with age. The treated paper has good ink receptivity and pencil receptivity as Well as good erasibility.

Example 2 A transparentized composition was made by mixing 25 parts by weight of the methylated methylol urea syrup of Example 1 with 25 parts by Weight of dicyclopentenyl alcohol, part by weight of p-toluene sulfonic acid and 50 parts by weight of isopropanol. A 13-pound weight 100% rag base tracing paper was impregnated with this composition and picked up 8.9% by weight thereof on the Weight of the paper. It showed a transparency of 40% and was similar in other respects to the paper of Example 1.

Example 3 Fifty parts by weight of the methylated methylol urea syrup of Example 1 is mixed with 50 parts by Weight of the monoglyceride of soya bean fatty acids obtained by transesterification of soya oil and glycerol. One-half part by weight of ethanesulfonic acid is added to the composition as a catalyst. A 12-pound 100% sulfite paper base was impregnated with the above composition and cured at 250 F. for 30 seconds. The resulting paper had somewhat less transparency than that of the previous two examples.

Example 4 An isopropylated methylol urea syrup was produced by a procedure analogous to that of Example 1 in which a mixture of 2.5 moles of formaldehyde with one mole of urea and about 0.8 mole of isopropanol was reacted.

Forty-two and one-half parts of the isopropylated methylol urea syrup was mixed with 42.5 parts of n-octyl alcohol, 1.5 parts of p-toluene sulfonic acid and about 15 parts of isopropanol. An 18-pound 100% rag tracing paper base was coated with the resulting composition, the excess squeezed OE, and the impregnated paper was then dried and cured at 250 F. for one minute. The resulting paper had a transparency approaching that of Example 2. Its surface was tack-free and it had good ink and pencil receptivity as well as good erasibility.

It is to be understood that changes and variations may be made without departing from the spirit and scope of the invention as defined in the appended claims.

We claim:

1. A method of transparentizing a paper sheet comprising impregnating the paper with a composition comprising a solution containing, dissolved therein at a concentration of at least 40%, a mixture consisting essentially of (1) 55 parts to 70 parts by weight of a compound selected from the group consisting of (a) monohydric alcohols having a hydrophobic hydrocarbon group of 8 to 24 carbon atoms and (b) monoglycerides of a fatty acid having from 8 to 24 carbon atoms and (2) 45 parts to 30 parts respectively by weight of a methylolated urea, the hydroxyl groups of which have been at least partially alkylated with alkyl groups selected from methyl, ethyl and isopropyl groups, and subsequently heating the impregnated paper at a temperature of F. to 250 F. for a period of a few seconds to several minutes to react the alcohol with the urea derivative at least until superficial tackiness is eliminated.

2. As a new article of manufacture, a transparentized paper obtained by the process defined in claim 1.

3. A method of transparentizing a paper sheet comprising impregnating the paper with a composition comprising a solution containing, dissolved therein at a concentration of at least 40%, a mixture consisting essentially of (1) 55 parts to 70 parts by weight of a compound selected from the group consisting of (a) monohydric alcohols having a hydrophobic group of 8 to 24 carbon atoms and (b) monoglycerides of a fatty acid having from 8 to 24 carbon atoms and (2) 45 parts to 30 parts respectively by weight of an at least partially alkylated methylolated urea compatible with said compound and obtained by a condensation reaction within a mixture of 1.5 to 3.0 moles of formaldehyde and at least 0.5 mole of an alcohol selected from methanol, ethanol, and isopropanol per mole of urea, and subsequently heating the impregnated paper at a temperature of 120 F. to 250 F. for a period of a few seconds to several minutes to react said compound with the urea derivative at least until superficial tackiness is eliminated.

4. As a new article of manufacture, a transparentized paper obtained by the process defined in claim 3.

5. A method of transparentizing a paper sheet comprising impregnating the paper with a composition comprising a solution containing, dissolved therein at a concentration of at least 40%, a mixture consisting essentially of 1) 55 parts to 70 parts by weight of a compound selected from the group consisting of (a) monohydric alcohols having a hydrophobic group of 8 to 24 carbon atoms and (b) monoglycerides of a fatty acid having from 8 to 24 carbon atoms and (2) 45 parts to 30 parts respectively by weight of at least partially methylated methylol urea compatible with said compound, and subsequently heating the impregnated paper at a temperature of 120 F. to 250 F. for a period of a few seconds to several minutes to react the alcohol with the urea derivative at least until superficial tackiness is eliminated.

6. A method as defined in claim 5 in which said compound is soya monoglyceride.

7. A method as defined in claim 5 in which said compound is dicyclopentenyl alcohol.

8. A method as defined in claim 5 in which said compound is n-octanol.

9. A method as defined in claim 5 in which said compound is glycerol mono-oleate.

10. A method as defined in claim 5 in which said compound is glycerol mono-stearate.

11. As a new article of manufacture, a transparentized paper obtained by the process defined in claim 6.

12. As a new article of manufacture, a transparentized paper obtained by the process defined in claim 7.

13. As a new article of manufacture, a transparentized paper obtained by the process defined in claim 8.

14. As a new article of manufacture, a transparentized paper obtained by the process defined in claim 9.

15. As a new article of manufacture, a transparentized paper obtained by the process defined in claim 10.

References Cited in the file of this patent UNITED STATES PATENTS 2,254,001 Conaway Aug. 26, 1941 2,291,079 Hoflerbert July 28, 1942 2,509,174 Scott et a1. May 23, 1950 

1. A METHOD OF TRANSPARENTIZING A PAPER SHEET COMPRISING IMPREGNATING THE PAPER WITH A COMPOSITION COMPRISING A SOLUTION CONTAINING, DISSOLVED THEREIN AT A CONCENTRATION OF AT LEAST 40%, A MIXTURE CONSISTING ESSENTIALLY OF (1) 55 PARTS TO 70 PARTS BY WEIGHT OF A COMPOUND SELECTED FROM THE GROUP CONSISTING OF (A) MONOHYDRIC ALCOHOLS HAVING A HYDROPHOBIC HYDROCARBON GROUP OF 8 TO 24 CARBON ATOMS AND (B) MONOGLYCERIDES OF A FATTY ACID HAVING FROM 8 TO 24 CARBON ATOMS AND (2) 45 PARTS TO 30 PARTS RESPECTIVELY BY WEIGHT OF A METHYLOLATED UREA, THE HYDROXYL GROUPS OF WHICH HAVE BEEN AT LEAST PARTIALLY ALKYLATED WITH ALKYL GROUPS SELECTED FROM METHYL, ETHYL AND ISOPROPYL GROUPS, AND SUBSEQUENTLY HEATING THE IMPREGNATED PAPER AT A TEMPERATURE OF 120* F. TO 250* F. FOR A PERIOD OF A FEW SECONDS TO SEVERAL MINUTES TO REACT THE ALCOHOL WITH THE UREA DERIVATIVE AT LEAST UNTIL SUPERFICIAL TACKINESS IS ELIMINATED. 